Pacemaker Lead Placement at Unusual Site: ECG Case

Watch the above case and try to solve the problem.

When looking at a paced rhythm on ECG, it often creates a pattern that can mimic bundle branch blocks, and this can sometimes be confusing. Most ventricular paced rhythms resemble a left bundle branch block (LBBB) pattern, with a broad QRS complex and a dominant negative deflection in lead V1, because the pacing lead is usually placed in the right ventricle and the impulse spreads across the septum from right to left. In contrast, a true right bundle branch block (RBBB) has an rSR′ pattern in V1 and a different overall axis. A paced rhythm will generally not look like a typical RBBB unless the lead is placed in an unusual site such as the left ventricle or coronary sinus branch. So, in practical terms, when you see pacing spikes followed by a wide QRS resembling LBBB, it usually indicates conventional right ventricular pacing.

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